A convulsive seizure induced by recurrent excessive firing of brain neurons is known to be attributed to various causes including not only central nervous system diseases, such as epilepsy and stroke, but also infections, such as encephalitis and meningitis, head injuries, acute alcoholism, and acute drug intoxication. In particular, if status epilepticus in which firing throughout the cerebral cortex lasts for several tens of minutes or longer from the start of the seizure occurs, an imbalance between metabolic and bloodstream is caused, which may lead to irreversible brain damage. Even if hypoxemia, hypoglycemia, or local circulatory disorder is not caused, the excessive neuroelectronic activity itself causes brain damage. Status epilepticus is therefore known to cause severe mental or neurological aftereffects due to this irreversible brain damage. Within a certain period of time after status epilepticus occurs, brain damage is less likely to be caused owing to a compensatory action; however, if treatment takes time, compensation becomes impossible, and severe brain damage is therefore likely to be developed. This evokes a need for treatment which terminates convulsions as soon as possible after the start of a seizure while an airway is promptly maintained.
The method most widely used for convulsive treatment is administration of a medicine by an intravenous injection or intramuscular injection which have an immediate effect. It is, however, difficult to safely give the injection to a patient being in a convulsive state. In addition, if a medicine is excessively administered, it is difficult to remove the medicine from the body, which causes the risk of unstable cardiorespiratory functions. Although attempts at easier methods have been also made, such as administration of a suppository and enema administration of an intravenous medicine, these methods have unsatisfactory immediate effects and are therefore unlikely to terminate convulsions at an early stage.
In contrast, there are medical findings that general anesthesia with inhalational anesthetics is the most effective for controlling status epilepticus and also has less serious side effects than other medications. In the findings, inhalational anesthetics can contribute to safe and steady administration of a medication to a patient being in a convulsive state to terminate the convulsion. Moreover, since the inhalational anesthetics are absorbed and eliminated through the lungs, the depth of anesthesia can be adjusted, which suggests that inhalational anesthetics are safer than other medications.
It is known that the administration of inhalational anesthetics involves use of a complicated inhalational anesthesia system including an anesthesia apparatus for generating mixed gas of carrier gas, such as oxygen supplied from a carrier gas source, and a volatile anesthetic to be vaporized with a vaporizer; a circular breathing circuit having a respirator for mixing the mixed gas generated by the anesthetic apparatus with the expired air of a patient and then transporting the resulting gas as intake gas of the patient; and a control unit having a computer for controlling these components (e.g., see Patent Literature 1).